Can someone give me a hint on why that happens and how to prevent that?
Thanks a lot!
Share the .skp file so we can see what you are working with. Usually when that happens it’s due to endpoints of the bordering edges being slightly out of plane.
Thanks for your fast reply! My upload fails due to the big file size. I already deleted all 3D-Warehouse-Models in my scene, but the file size hasn’t changed. Can i remove the downloaded models somehow from the .skp?
Upload it to DropBox or WeTransfer and share the link.
Simply deleting them from the model space doesn’t remove them from the file. You need to purge unused content. Go to Window>Model Info>Statistics and click on Purge Unused.
UmbauSchwabering ONLINE.skp (2.0 MB)
Purge helped, thanks!
UmbauSchwabering ONLINE-mitFläche.skp (2,1 Mo)
Hi, I just removed the two triangles and drew a rectangle in their place… it is now a flat plane.
I’m just curious, why are the walls not grouped/componented so as to distinguish them from these “ceiling” rectangles ? ?
& if you render hidden geometry visible there are lots of odd lines…
Anyway, I’m pretty sure the issue is with not having grouped the lines & planes that form your walls…
Best of luck
There are some things in your model but I’ll leave it in @paddyclown’s hands.
Dave, please weigh in here if I’ve missed something ! 
Thanks for your replies @paddyclown and @DaveR. The reason why I haven’t grouped them is just because I didn’t know that is necessary or helpful. Disclaimer: I come from the CAD world (AutoDesk, Catia, …) and just started using SketchUp 2 days ago.
What would be the correct way or logic to grouping those elements?
@DaveR if you don’t mind, I’d be very interested in your findings as I’m right at the beginning of learning SketchUp and happy about all input I can get!
@max2 - well, from experience, it’s always best to create groups/components of anything that you want as homogeneous but separate geometry.
As in, you probably want to separate a wall from a floor, from a door & from a ceiling so that everything isn’t just all stuck together like chewing-gum 
So as soon as you’ve extruded your wall from the plan view (I assume that’s what you did) you’d turn it into a component (especially if you want to classify it as an ifcWall or whatever) and then pop it onto the “tag” that you want for wall objects…
Ok yes, that absolutely sounds useful. I’ve got a lot of hickups due to not having done that 
Is there any chance that I can group / componentize my current setup now, or do I need to start over?
toto24.skp (2,5 Mo)
Here is a small file that I give to young staff who are starting out with SketchUp to show them how I like to structure a file & classify objects…
OK. So the diagonals appear to be formed due to the lack of grouping of the geometry and the loops of edges being broken in the plane of the edges. With Hidden Geometry turned on those diagonals can be erased.
You should be making groups or components of discrete objects; walls, floor, ceilings. I also notice incorrect tag usage.
You should edit the Units and turn off Length Snapping. As it is you have length snapping enabled with a 1mm increment. This can lead to errors in your modeling, especially as 1 mm isn’t precise enough for endpoint alignment.
Notice that the windows have some issues with hidden geometry. That should be cleaned up.
Since you are just getting started with SketchUp I would suggest taking the time to go through the instructional tutorials at learn.sketchup.com . Don’t try to make SketchUp work like other CAD programs. That’ll just lead to frustration.
well, either route will take up time… as a learning experience, try both !
See, I knew @DaveR would give you some great pointers… & yes, the tuto’s are really helpful when you’re at the start of your SU journey !
Thanks a lot both of you, I really appreciate your feedback! I’ll have look at both the example-file as well as the tutorial videos with focus on grouping, components etc… I already did a quick hop-through, but I guess I underestimated the differences between what I’m used to working with and SketchUp.
A lot of people do that. Once you learn the correct workflow in SketchUp you’ll find the whole process much easier.
wow, a lot of plugins you’ve got there
Thanks for the explanation, merci beaucoup!
@max2 Yup, viel Plugins, genau… Und Bitte sehr
